I have a friend with an X45 and his has the 8.1 450hp. And believe me when I say...it NEEDS it! It is a big boat, and if you put any weight in it it'll take the hp to push it. An upgraded prop would help too. IMO that's just too much boat. He's had many probs with the boat running gear wise bc its just so much weight to push around and maneuver through the water.